Convert GSLIDES to PPTX

Converting Google Slides Shortcuts directly to Microsoft PowerPoint Presentations (.gslides to .pptx conversion) is, per se, not possible, since the .gslides shortcuts do not contain any multimedia data. They merely link to an existing Google Slides object located on your Google Drive. 

Simply open your presentation using the .gslides shortcut, then download it in a .pptx format via the 'File -> Download As' function.